Fossils and Past Lives

Body fossils

Fossilised hard parts of an organism such as the skeleton or shell

How original composition affects fossilisation

Fossils made of calcite or aragonite altered easily, silica may be preserved unaltered

How energy levels affects fossilisation

High energy fragments the organism, low energy levels means better preservation

How transport distance affects fossilisation

Further transport distance means more collisions resulting in worse preservation

How speed of burial affects fossilisation

More rapid burial reduces exposure to scavengers

How amount of oxygen affects fossilisation

No oxygen means aerobic bacteria cannot decay the organism

How size of sediment affects fossilisation

Fine sediment means better preservation as smaller particles cause less damage

How diagenesis affects fossilisation

Composition of groundwater can affect the fossilisation process or dissolve the fossil

Replacement preservation

Atom by atom exchange of the original mineral hard part with a mineral of another composition

Polymorphs

Minerals with the same composition but different crystalline structures

Aragonite and calcite are

Polymorphs with formula CaCO3

Aragonite

Unstable mineral that makes up shells and corals

Calcite

Stable mineral that replaces aragonite over time

Silicification

Silica crystallises out of groundwater solution and fills holes left by organism

Silicification of wood, shell or bone

Silica fills pores increasing density or resulting rock

Pyritisation

Replacement of original material by iron pyrites in anaerobic conditions

Carbonisation

Process of burial removes volatiles leaving a fine film of carbon

Moulds

Impression of the outside or inside of a fossil in sediment

Casts

Fossil void filled by another mineral

Exceptional preservation

Fossils with very fine detail such as soft tissue

Factors affecting chance of fossilisation

Abundance of organism, habitat, size of organism

Amber preservation

Tree resin becomes very hard and is completely anoxic, so the organism remains completely intact

Tar preservation

Water accumulates on top of surfaced hydrocarbons, animals fall in, very anoxic conditions

Burgess Shale

Canadian fossil formation from Cambrian lagoon with low energy and anoxic conditions

Trace fossils

Preserved evidence of the activity of the organism

Formation of trace fossil

Imprints in soft sediment later infilled by more sediment

Benthonic

Organism lives on or in the sediment substrate of the sea floor

Infaunal

Living within the sea floor

Epifaunal

Living on top of or attached to the seafloor

Vagrant

Moves around on the sea floor

Sessile

Remains attached to the surface where it lives

Pelagic

Organism that lives in the water column

Planktonic

Describes organisms that are freely floating in water

Nektonic

Organisms actively swimming in the water column

Fossil assemblage

Many types of organism found together

Death assemblage

Organisms found not in their living position, having been moved, broken etc.

Life assemblage

Organisms preserved as they would have lived

Derived fossils

Fossils found in one rock, weathered out and re-deposited in a younger sediment

Articulated fossil

Organisms found whole or connected as in life

Coral phylum

Cnidaria

Corals class

Anthozoa

Coral inner layer

Endoderm

Coral outer layer

Ectoderm

Nematoblasts

Coral stinging cells

Coral skeleton

Calcium carbonate

Polyp

Soft bodied organism inside coral

Corallum

The whole skeleton of a solitary or colonial coral

When did corals first evolve?

Cambrian period 540ma

Solitary coral

Singular polyp which secretes a single skeleton

Compound coral

Many polyps living in communal fashion with many skeletons fused together

Calice

Bowl shaped depression where the soft polyp sits

Epitheca

Outermost layer of the coral skeleton

Tabula

Horizontal plate dividing the corallite skeleton

Corallite

The skeleton produced by one coral polyp

Growth lines

Wrinkles produced as the coral grew

Columella

Axial rod which supports the septa, running up the centre of some corals

Dissepiments

Curved plates connected to septa and tabulae

Septa

Vertical plates, radially dividing the corallite, may be major or minor

Rugose coral shape

Horn shaped

Tabulate coral shape

Columnar pentagons

Scleractinian coral shape

Branched tubes

Rugose geological range

Ordovician to Permian (extinct)

Rugose tabulae

Always present

Rugose size

Large

Rugose dissepiments

Sometimes present

Rugose symmetry

Bilateral (one plane)

Rugose columella

Always present

Rugose septa

Major septa at 6 points with 4 sets of minor septa

Rugose colonial/solitary

Colonial or solitary

Rugose mural pores

None

Mural pores

Connections between adjacent corallites, perhaps for communication

Tabulate geological range

Cambrian to Permian

Tabulate tabulae

Present and well developed

Tabulate size

Small

Tabulate dissepiments

None or sometimes reduced

Tabulate symmetry

Radial (many planes)

Tabulate columella

Not present

Tabulate septa

Sometimes present but reduced

Tabulate colonial/solitary

Always colonial

Tabulate mural pores

May be present

Scleractinian geological range

Triassic to present (extant)

Scleractinian tabulae

Always present

Scleractinian size

Small

Scleractinian dissepiments

Always present

Scleractinian symmetry

Radial (many planes)

Scleractinian columella

May be present

Scleractinian septa

Major septa at 6 radial points

Scleractinian colonial/solitary

Colonial or solitary

Scleractinian mural pores

None

Zooxanthellae

A type of algae that lives inside modern day corals

Symbiotic relationship

Describes two organisms living together for mutual benefit

Polyp feeding

Food particles extracted from water, either by paralysis from stinging cells or entrapment in mucus

Conditions for coral growth

Less than 30m below water level, clear water, high energy, marine, temp. 23-27 degrees

Fringing reef

A reef growing in the shallow waters surrounding land

Barrier reefs

As land shrinks or sinks the reef becomes further from the land

Atoll

Volcano sinks, leaving a ring of coral with a lagoon in the middle

Brachiopod phylum

Brachiopoda

Brachiopods mode of life

Benthonic, sessile

Brachiopods periods

Cambrian - present (extant)

Brachiopods near extinctions

Permian-Triassic and Triassic-Jurassic extinction events